1. Field of the Invention
This invention relates to systems of power generation and more particularly to a system of employment of the latent heat of fusion of water in power generation and water purification, especially desalination.
2. Description of the Prior Art
It is well known that conventional fossil-fuel sources of energy, especially the convenient sources, petroleum and natural gas, are in limited supply, and that the use of nuclear energy to generate power faces the opposition of those who fear nuclear accidents, the latent dangers in nuclear waste, and thermal pollution by effluent cooling water. A need consequently has long been felt for means to supplement the three major but exhaustible energy sources, e.g. petroleum and (or) natural gas, coal and nuclear fuels. Vast expenditures have been made to establish the energy levels at which nuclear fusion will become a reality; and direct utilization of solar energy continues slowly to develop within its limits of practicability. Where modest demands for energy, such as home heating, need be met, heat pumps are frequently employed and are of numerous system configurations as shown by the examples hereinafter given; these all require an auxiliary power supply and consequently continue to rely on one of the aforesaid major energy sources. Power units using temperature differentials of a fluid directly (as opposed to the indirect differentials between boiler and condenser created by combustion of a fossil fuel) have also been developed and, except in peculiar circumstances as in geothermal heat, found impractical primarily because of the low Carnot (theoretical) efficiency. Limitations of systems so far devised are such that practical considerations of pumping, friction, initial investment, debt service, and maintenance overcome the margin of energy recovery attainable.
Closely related to the world-wide short supply, limited reserves, or poor distribution of major fuel sources is the equivalent situation respecting fresh water. Numerous systems have been developed for recovery of fresh water and again their usefulness has been limited to the above-mentioned considerations or, as otherwise expressed, the power requirements of the systems.
A survey of the efforts made and progress so far attained in using the energy available in thermal differences between ocean water at its surface and at its depth is to be found in Ocean Thermal Energy Conversion (OTEC), edited by Knight, Nyhart, and Stein, copyright by the American Society of International Law, published by D. C. Heath and Co., Lexington, Mass., (1977), 251 pp. especially in Chapters 1 and 2. Available ocean-water temperature differences are at most about 22.degree. C., "which results in a very low theoretical Carnot efficiency of the thermodynamic cycle, namely about 6 percent." In another example, the theoretical Carnot efficiency of the OTEC system is given at 3.3% in OTEC System Study Report, Trimble, L. C. et al., Proceedings, 3rd Workshop on OTEC, pp. 3-21, Houston, Texas, May 8-10, 1975, published by the Johns Hopkins University.
In U.S. Pat. No. 4,006,595 to Forbes, a Freon ("FREON" is a registered trademark of E. I. duPont de Nemours and Company for refrigerants; the word is used herein with initial capitalization in recognition of same,) working fluid is employed to power a gas-sealed, flywheel turbine in a system which employs unidentified thermal differences to vaporize the Freon contained in two tanks which alternately supply liquid Freon to a heater, the fluid being transferred thereto in the system by capillary means connected to a high-pressure outlet of the turbine.
Baldwin U.S. Pat. No. 3,531,933 discloses and claims another power system in which the working fluid is a Freon-type refrigerant (dichlorodifluoromethane), and which uses ethylene glycol as a coolant and flooded-type evaporation to condense the working fluid vapors exhausted from a reciprocating piston engine operated by the system.
Numerous patented systems rely on the energy availability of temperature differentials to provide motive power. Siegel U.S. Pat. No. 3,846,984 relates to a temperature-gradient fluid motor which consists of a pair of sealed chambers containing a low boiling fluid with a means for obtaining a temperature gradient between the chambers (one immersed in water, one in cooler atmosphere).
U.S. Pat. Nos. 3,945,218 and 3,953,971 both relate to power systems that utilize elevation differences and available temperature differences on the earth's surface, and that also convert geothermal energy to useful work.
Pecar U.S. Pat. No. 3,987,629 discloses another sealed system for producing motive power from small temperature differentials and contemplates vaporization of part of a working fluid and operation of a turbine by the remaining fluid moved by the kinetic energy of the vapor.
Williams U.S. Pat. No. 4,086,772 discloses a system for converting thermal to mechanical energy including a tube having a plurality of flow converging zones alternating with a plurality of flow diverging zones to vaporize at least part of a working fluid such as carbon dioxide, liquid nitrogen, or flourocarbons and converting part of the energy of the vapor stream in a turbine to mechanical shaft work. Energy is supplied to the system by an ambient thermal energy source, such as wastewater, consisting of a body having a temperature differential with the condensed fluid in the system.
DeMunari U.S. Pat. No. 4,100,744 utilizes thermal differentials such as exist in ocean waters, as mentioned in the above references to the OTEC system, in a thermodynamic cycle that transforms the kinetic energy of the working fluid into mechanical energy.
Cheng et al. U.S. Pat. No. 3,354,083 makes use of the well-known anomaly that water melts at lower temperatures under higher applied pressure in contrast to usual liquids. Pressures of 150 to 200 atmospheres are applied to ice, which melts, and to a selected exchange medium, which freezes. Resulting low-temperature, high-pressure fresh water is employed to operate a turbine and to cool a feed solution, and the resulting solidified exchange medium is brought at atmospheric pressure into contact with additional saline water.
A carefully balanced and well developed thermodynamic system and combination of systems is disclosed in Brola U.S. Pat. No. 4,118,934 for transforming heat at relatively low temperature into power or energy, as in environmental conditioning apparatus. The said heat can be in waste gases, cooling waters from condensers, or other form of low grade energy and its recuperation into power is accomplished by a two-fluid thermodynamic cycle.